Interconnection substrates or components, such as interposers are used in electronic assemblies for a variety of purposes such as to facilitate connection between components with different connection configurations or to provide needed spacing between components in a microelectronic assembly, among others. Interposers can include a semiconductor layer, such as of silicon or the like, in the form of a sheet or layer of material having conductive elements such as conductive vias extending within openings which extend through the layer of semiconductor material. The conductive vias can be used for signal transmission through the interposer. In some interposers, ends of the vias can be exposed and usable as contact pads for connection of the interposer to other microelectronics components. In other examples, one or more redistribution layers can be formed on interposer on one or more sides thereof and connected with one or both ends of the vias. A redistribution layer can include numerous conductive traces extending on or within one or more dielectric sheets or layers. The traces can be provided in one level or in multiple levels throughout a single dielectric layer, separated by portions of dielectric material within the layer. Vias can also be included in a redistribution layer to interconnect traces in different levels of the redistribution layer.
An example of such an interposer 1 is shown in FIG. 1A, which shows vias 3 extending through the substrate 2. The semiconductor material of the substrate 2 can be insulated from the vias 3 by a barrier layer 4 positioned therebetween. A redistribution layer 5 is shown having routing circuitry 6 therethrough. Even with the barrier layer 4 present, structures employing semiconductor material for substrate 2 can exhibit problematic levels of insertion loss through vias 3 due to impedance created therein by the capacitive qualities of the semiconductor material, for example, particularly in the areas between vias 3. This phenomenon is represented in FIG. 1B, which shows an example circuit diagram showing the effect of the capacitance and resistance of the semiconductor material of substrate 2, which in the area 7, causes impedance within the signal vias 3. The resulting insertion loss can impair the performance or reliability of such interposers and, accordingly, systems in which they are included, particularly when high-frequency signals are transmitted therethrough.
Some interposers are used as components of microelectronic assemblies. Microelectronic assemblies generally include one or more packaged microelectronic elements such as one or more semiconductor chips mounted on a substrate. The conductive elements of the interposer can include the conductive traces and terminals that can be used for making electrical connection with a larger substrate or circuit panel in the form of a printed circuit board (“PCB”) or the like. This arrangement facilitates electrical connections needed to achieve desired functionality of the devices. The chip can be electrically connected to the traces and hence to the terminals, so that the package can be mounted to a larger circuit panel by bonding the terminals of the circuit panel to contact pads on the interposer. For example, some interposers used in microelectronic packaging have terminals in the form of exposed ends of pins or posts extending through the dielectric layer. In other applications, the terminals of an interposer can be exposed pads or portions of traces formed on a redistribution layer.